How did they crack the technical challenge of 'pre-pressing before printing,' and what's innovative about this process?

As the packaging and printing industry continues to demand higher production efficiency, cost, and printing quality, the limitations of products using the traditional "stamp first and print later" process have become increasingly apparent as their scale grows. Because they use hot stamping first for holographic electrochemical aluminum before printing, they face issues such as low production efficiency, insufficient registration accuracy, high material waste, and complex processes. To address the above issues, this paper proposes a holographic positioning reel paper gravure printing technology, adopting a continuous roll paper production method, combining holographic film pressing, registration cursor recognition, and dynamic tension control to achieve high-precision and efficient printing. This technology can be widely applied in cigarette packs, liquor boxes, high-end cosmetics packaging, and other fields, with significant industrial application prospects.

Holographic positioning roll paper combined printing process

The holographic positioning roll paper combined gravure printing method proposed in this study mainly includes three steps: First, the roll paper is pressed into positioning paper by a holographic film press machine, with laser laser graphics and registration cursors preset on the paper surface; Next, the pressed roll paper is rewound and placed into the roll press press; Finally, registration printing of printed images and text is performed through registration light marking. Compared with traditional sheet-fed paper processes, this method has significant advantages by using roll paper as the printing medium and adapting to roll paper printing machines, greatly improving the processing speed of paper products; By replacing the original pre-gauge and side gauge registration methods with cursor registration, product accuracy and quality are significantly improved.

Roll positioning paper is a key step in combined printing, and its process includes several detailed steps: first, laser engraving technology is used to produce positioning anti-counterfeit metal masters, which serve as standard templates for film preparation. Then, using PET photonic film as the base material, a coater is used for primer coating. Next, a holographic positioning laser transfer film is pressed onto a holographic film press, which is printed with the laser laser graphics and registration cursor required for the printed material. Next, the PET photonic film substrate with imprinted holographic positioning laser transfer film is placed into a high-vacuum aluminum plating machine for surface vacuum aluminization. Finally, on the laminating machine, the vacuum-plated PET photonic film substrate is stripped and compounded, coated with a protective or color-developing layer, and humidified to produce positioning laser paper. This series of processes ensures high-precision production of graphics, text, and registration cursors.

Holographic positioning roll paper combined for printing

Analysis of technical difficulties

In practical applications, holographic positioning web paper gravure printing technology mainly faces technical challenges in film making, lamination, and printing registration.

01/ Challenges in controlling the film-making process

(1) Substrate expansion and deformation: The expansion rate of BOPP/PET luminous films varies between batches, and during coating and molding, temperature and tension further deform, leading to unstable holographic pattern dimensions.

(2) Thermal deformation of molding: High-temperature molding (120~180°C) can easily cause the film to stretch, causing changes in the spacing of holographic patterns, which affects registration in subsequent processes.

(3) Accumulation of aluminum plating errors: Fluctuations in winding tension during the aluminum plating process lead to increased positioning deviations of the holographic pattern.

02/ Control Challenges in the Holographic Positioning Roll Paper Film Lamination Process

(1) Tension matching issue: The tension between the film and paper is mismatched, which can easily cause wrinkles or stretch deformation of the composite material.

(2) Paper moisture effect: Changes in temperature and humidity cause the paper to stretch, contract, and deform, causing the holographic pattern to shift position.

(3) Sticking pattern defects: Uneven lamination may cause reduced brightness or surface defects in holographic patterns, increasing the defect rate.

03/ Control Challenges in the Holographic Positioning Roll Paper Printing Process

(1) Paper thermal deformation: During the printing drying process, the paper expands and contracts due to heat, making registration more difficult.

(2) Holographic and printed text matching: It is necessary to ensure that the gravure graphics and text fully coincide with the prefabricated holographic pattern, with errors controlled within ±0.1mm.

Holographic positioning roll paper combined printing

Application solutions

To address multiple technical challenges in film production, lamination, and printing stages, this study proposes the following innovative solutions through in-depth research and innovative optimization of key processes.

01/ Optimized design of the registration cursor

To improve registration accuracy, the holographic positioning roll paper cursor was optimized based on the registration requirements of gravure printers and the photoelectric recognition principle. Traditional solid-shaped registration cursors are produced by hot stamping, and their surface is less readable by the electric eye than those produced by ink printing. To solve this problem, this method uses a hollowed-out registration cursor on one side of the paper tape, as shown in Figure 1. During testing, the registration between gravure color groups was accurate and stable, with a deviation of ≤± 0.1mm in registration accuracy. Therefore, this design allows the gravure printer's eye to perform registration work against the hollowed cursor, significantly improving the stability and accuracy of the registration.

Figure 1 shows an alignment cursor with a hollow structure set on one side of the paper tape.

02/ Improvements and Optimization of the Reel Paper Printing Machine

(1) A fixed-length stretching (pre-alignment) device is added to the unwinding unit of the printing machine, as shown in Figure 2. To meet the process requirements of laminating before printing, this study made several improvements and optimizations to the reel paper printing machine. First, a fixed-length stretching (pre-alignment) device was added to the unwinding unit of the printing machine to adjust the expansion and contraction of the reel paper caused by lamination. This device includes traction rollers driven by independent servomotors, photoelectric eyes, compensating rollers, and paper guide rollers, enabling real-time adjustment of paper tension based on alignment cursor information to ensure printing accuracy.

Figure 2: Adding a Fixed-Length Stretching (Pre-Registering) Device to the Rewinding Unit of the Printing Press

(2) Key parameters were determined through experiments: The circumference of the paper web on the plate cylinder should be the theoretical value multiplied by the deformation factor (0.9399–0.9699); the circumference of the first-color plate cylinder on the web gravure press should be the theoretical value multiplied by (1 + deformation factor), with the deformation factor preferably 1.0‰–1.5‰; the circumference of the web die-cutting cylinder should be the theoretical value multiplied by the deformation factor, preferably 1‰–4‰.

The laser-positioned plate paper web is installed on the rewinding unit of the gravure press. The press pulls the web into the first printing unit, where dual photo-eyes at the output of the first printing unit simultaneously collect information from the holographic registration marks and the printing registration marks. The computer compares the collected data, analyzes the position of printed images, and if there is a deviation, it adjusts the rotation speed of the first printing unit's motor to correct the error. Once the position reaches the preset value, image printing begins. These optimizations effectively solve the problem of excessive distance errors between holographic images and printed images during printing.

Through systematic process optimization and technological innovation, this study successfully overcame the core challenges of holographic registration on web gravure presses, significantly reducing material and labor costs associated with flatbed and offset processes, providing the packaging printing industry with an efficient, accurate, and reliable solution. As the process continues to improve and equipment is upgraded, this technology is expected to achieve large-scale applications in more high-end packaging areas, driving the industry toward smarter and greener practices.